There is proposed a coupling structure in which one of two coupled components has a frame part, the other has two pieces and an upper surface of one of the two pieces has an engaging angled part (refer to Patent Document 1). The frame part enters between the two pieces. One of the two pieces engages an edge of one of two components located at a protruding bottom of the frame part with the engaging angled part. In such coupling structure, when a force in separating direction is applied to the two coupled components, a high resisting force (pulling force) can be ensured. However, as the pulling force becomes higher, a resisting force (inserting force) is higher.